Integrated circuit chip manufacturers fabricate semiconductor devices by sequentially applying and patterning layers of usually not more than 1 .mu.m thick to a semiconductor wafer. The device layers may comprise various materials such as insulating layers in addition to one or more of the following conductive layers: a thin metal film such as tungsten, aluminum, copper, or titanium; a thin polycrystalline silicon (polysilicon) coating doped with impurities; or other layers of metal silicides and metal nitrides. Process control and manufacturing tolerances apply to the various device fabrication processes. Deviations from specified target tolerances in excess of only a few percentage points may result in defective and rejected semiconductor chips.
Semiconductor device manufacturers can only discard rejected semiconductor chips, thus resulting in undesirable production process waste and increased device manufacturing costs. If it is possible, however, to closely monitor various process parameters in-situ during the process or immediately after processing each individual wafer, process parameters can be properly adjusted in order to achieve good process control and improved process parameter reproducibility. Thus, the need exists for accurate methods and sensors to measure physical parameters in-situ during or immediately after processing each semiconductor wafer.
Methods for applying polycrystalline layers on semiconductor wafers include processes known as chemical-vapor deposition (CVD), evaporation, and physical-vapor deposition (PVD) or sputtering. These thin film deposition processes usually take place in a low-pressure deposition chamber filled with process gases using thermal, photo or plasma activation to generate the necessary species for deposition of layers such as refractory metals or aluminum. To maintain layer uniformity across an individual semiconductor wafer surface, as well as process repeatability from wafer to wafer during the processing of many wafers, it is important to know the thickness of the polycrystalline layer deposited on the wafer. However, known methods of measuring layer thicknesses on semiconductor wafers mostly require physical contact with the layer. But, physical contact with a wafer in the processing reactor can be detrimental to the process or wafer and may reduce the device manufacturing yield. Therefore, there is a need for a non-invasive method and apparatus for measuring the thicknesses of layers and other physical characteristics of semiconductor wafers.
Physical properties of semiconductor wafer layers and the semiconductor substrates themselves that a sensor should measure include the following:
(1) thickness measurements of CVD metal films;
(2) thickness measurements of other polycrystalline films;
(3) roughness and reflectance measurements of the semiconductor wafer or conductive layer surface;
(4) spectral emissivity measurements of the semiconductor wafer; and
(5) background doping concentration measurements of the wafer.
There are no known methods or systems for in-situ non-invasive measurements of the above properties for monitoring physical parameters of the semiconductor wafers during, before, or after a device fabrication process. In particular, there is not presently a low-cost non-invasive sensor that can provide in-situ pre-process or post-process thickness measurements for CVD metal films or other polycrystalline films such as polycrystalline silicon. Moreover, although some measurement systems can provide off-line surface roughness and reflectance measurements of semiconductor wafer surfaces, no known sensor system can provide such comprehensive measurements in-situ either immediately prior to or following a CVD or other deposition or etching process. Additionally, there is no low-cost compact reliable sensor that can fit within a semiconductor wafer processing reactor to provide non-invasive in-situ measurements of layer thickness, surface roughness and reflectance, spectral emissivity, and background doping of semiconductor wafers.
Thus, there is a need for a non-invasive system that can provide thickness measurements of metal films and other polycrystalline films on semiconductor wafers.
There is a need for a non-invasive in-situ sensor for performing thickness measurements of metal films and other polycrystalline films on a semiconductor wafer immediately before and after a deposition, etching, or other fabrication process (e.g., high-temperature CVD).
There is yet a need for a sensor that can provide surface roughness measurements of semiconductor wafers.
There is still a need for a sensor that can provide spectral emissivity measurements of semiconductor wafers.
Moreover, there is a need for an inexpensive and compact sensor system that can provide all of the above measurements as well as uniformity data. Furthermore, a need exists for a low-cost compact sensor that can measure metal or polycrystalline film thickness, surface roughness and reflectance, and spectral emissivity that is non-invasive and can be mounted in a semiconductor wafer processing reactor or wafer metrology chamber.